1. Field of the Invention
The present invention relates to a wobbling signal demodulation method, a wobbling signal demodulation circuit, and an optical disk drive; and particularly, a wobbling signal demodulation method and a wobbling signal demodulation circuit for demodulating a wobbling signal obtained based on light reflected from a recording surface of an optical disk, and an optical disk drive having the wobbling signal demodulation circuit.
2. Description of the Related Art
Along with progress in digital technology and data compression technology, optical disks, such as a CD (Compact Disk) and a DVD (Digital Versatile Disk), which has the same diameter as the CD but a capacity seven times larger as that of the CD, are attracting attention as media for recording data of music, movies, photos, computer software, and other user data. In addition, because of the lowered price of the optical disks, an optical disk drive equipped with such an optical disk is widely used.
Generally, wobbling tracks are formed on a recording surface of a write-once optical disk, such as a CD-R (CD-recordable), a DVD-R (DVD-recordable), and a DVD+R (DVD+recordable), or a rewritable optical disk, such as a CD-RW (CD-rewritable), a DVD-RW (DVD-rewritable), and a DVD+RW (DVD+rewritable). The wobbling tracks include portions modulated according to a specified modulation scheme, and information is included in the modulated portions (reference can be made to Japanese Laid-Open Patent Application No. 10-69646). For example, in a DVD+R or a DVD+RW (below, simply abbreviated to be “DVD”), address information is included in the modulated portions by means of phase modulation.
In an optical disk drive supporting a DVD+R or a DVD+RW, when recording user data in the optical disk, a light beam from a light source is emitted on the recording surface of the DVD+R or the DVD+RW and the incident light is reflected at the recording surface; a wobbling signal, which corresponds to the wobbling shape of the tracks, is detected from the light beam reflected on the tracks, and a clock signal is generated from the wobbling signal; then the wobbling signal is demodulated in synchronization with the clock signal, thereby the address information is obtained. Then, the recording position is controlled based on the obtained address information and the clock signal.
Optical disk drives having circuits capable of phase demodulation on the wobbling signal have been proposed, for example, in Japanese Laid-Open Patent Application No. 2002-74660, Japanese Laid-Open Patent Application No. 2002-124043, Japanese Laid-Open Patent Application No. 2003-157537, Japanese Laid-Open Patent Application No. 2003-203356, Japanese Laid-Open Patent Application No. 9-297969, and others.
Recently and continuing, in order to reduce the size of the optical disk drive, it is attempted to integrate circuits including the phase demodulation circuit into one chip (LSI) to increase the degree of integration of the circuits.
In the LSI, a digital part for processing digital signals and an analog part for processing analog signals are separated formed, and the phase demodulation circuit is in the digital part. In this circuit, the wobbling signal, which is an analog signal, is converted into a digital signal in an analog-digital (AD) converter, and is then provided to the phase demodulation circuit. For example, assume the number of times of sampling in one period of the wobbling signal in the AD converter is 16, and if the optical disk rotates at a one-time speed, the period of the wobbling signal is 1.22 μm, and the wobbling signal is sampled once every 75 ns in the AD converter.
Along with the spreading use of the optical disks, it is required to increase the recording speed on the optical disks. However, if the recording speed is further increased, for example, if the optical disk rotates at a 16-times speed, the period of the wobbling signal becomes 76.5 ms, and the wobbling signal is sampled once every 4.78 ns in the AD converter. In order to meet this requirement, a fast AD converter is needed and this causes an increased cost.